Whole-breast external beam radiotherapy has been clinically demonstrated to reduce the risk of disease recurrence. While the benefits of radiotherapy are many and the associated rates of risk are low, the effects of those risks can be severe. Typical treatment workflow begins with computed tomography (CT) scan, followed by the creation of a patient-specific treatment plan that uses static or dynamic radiation beams to target a prescribed dose at the tumor and minimize dose to healthy tissues. Fractionated therapy is delivered on a daily basis for up to several weeks; the patient is meticulously positioned on the treatment bed as close to the original CT position as possible, to operate under the assumption that the treatment will be delivered as planned if this alignment is accurate. The radiation oncology team uses many tools to ensure high levels of quality assurance, however, none of these technologies have yet provided the ability to physically view the beam on the surface of the patient, and thereby eliminate the implied assumption with directly observed evidence. Cherenkov imaging seeks to fill this gap in the treatment workflow of 'on patient' dosimetric imaging. The first in vivo observations of the radiation field on the skin of patients using Cherenkov imaging were documented after a pilot clinical trial of 12 patients; a second clinical trial of up to 70 patient is currently underway. Cherenkov imaging provides the opportunity for a new treatment verification process that will offer novel information to clinicians about features such as surface dose over the targeted region and precise beam shape, and could ultimately improve patient safety. Still, there is a current limitation on the method which requires time-consuming post-processing of the acquired clinical images. The impetus of this proposal is to build a prototype Cherenkov imaging system that operates and displays images in real-time, in order to physically monitor the beam on the patient during treatment as it is being administered. The real-time system will have the potential to detect abnormalities in the treatment which would otherwise go unnoticed. This will be evaluated by several layers of use, starting with medical physics evaluation, then radiation therapist survey of use, and then oncologist confirmation of targeting. To allow effective and efficient use of the system in the clinic, the entire system will be developed with input from a carefully selected advisory team consisting of Dr. Jarvis (Radiation Oncologist), Dr. Gladstone (Chief Medical Physicist), and Mr. Craig Hansen (Chief Radiation Therapy Technologist). The proposed system will allow for a completely non-invasive, non-disruptive investigation of factors such as multi-leaf collimator pattern tracking, patient alignment, and correlation between Cherenkov intensity and surface dose for relative quantification and careful monitoring by physicians. During this project, the PI Jacqueline Andreozzi will be trained in many aspects of radiation therapy, breast cancer management, and statistical analysis of outcomes, which make up key components of this project and her career goals. Weekly, monthly and annual goals on training augment a cutting edge research project.